1. Field of the Invention
The present invention relates to a method and an apparatus for bend-shaping a glass plate for windows for transporting machines such as automobiles, ships, airplanes and windows for buildings, in particular, for windows of automobiles.
2. Discussion of Background
In recent years, there has been used a glass plate having radii of curvature not only in a single direction but also plural directions (hereinbelow, referred to as a complexly curved glass plate) in a window for an automobile For example, U.S. Pat. No. 4,123,246 discloses a method for forming such complexly curved glass plate. The specification of the patent describes a method for forming a complexly curved glass plate by transferring by means of a plurality of rollers a glass plate heated to the nearly softening temperature in a heating furnace.
In this case, the glass plate softened by heating is transferred by the rollers wherein the central portion of each of the rollers are curved downward in a direction perpendicular to a transferring direction (hereinbelow, referred to as a transfer perpendicular direction). Then, the central portion of the glass plate drops due to its dead weight whereby it is bend-shaped in the transfer perpendicular direction so as to follow a radius of curvature of the curved rollers. Further, the plurality of curved rollers are arranged to have an inclination in the transferring direction. When the glass plate is transferred on the curved rollers, it is bent so as to follow the inclination of the curved rollers whereby bend-shaping is conducted to the glass plate with respect to the transferring direction. Thus, the glass plate is bend-shaped in the transferring direction and the transfer perpendicular direction whereby the complexly curved glass plate having radii of curvature in two directions is formed.
The complexly curved glass plate after having been bend-shaped is transferred to a cooling device where it is quenched and toughened by cooling air blasted from the cooling device.
The method described in the above-mentioned specification has the problem as follows. A contacting surface area between the complexly curved glass plate bend-shaped and the rollers tends to decrease. In transferring the complexly curved glass plate, therefore, the gravity center of the complexly curved glass plate is sometimes shifted toward the deepest portion of the curved rollers. Accordingly, the complexly curved glass plate may shift in the transferring direction and the transfer perpendicular direction, and may turn on the curved rollers.
On the other hand, for the purpose of substantially uniformly cooling the complexly curved glass plate, the cooling device is so constructed as to adjust the position and the height of nozzles for blasting cooling air depending on a shape of the complexly curved glass plate. In this case, the position and so on of the nozzles of the cooling device are determined on the premise that the complexly curved glass plate is transferred in a state free from turning. Accordingly, when the complexly curved glass plate is transferred to the cooling device in a state of turning on the curved rollers, the turning complexly curved glass plate partially comes closer to or separate from the nozzles.
Since efficiency for cooling the complexly curved glass plate depends on a distance between the nozzles and the complexly curved glass plate, a portion easily cooled and a portion difficult to cool are produced in the turning complexly curved glass plate. As a result, a temperature distribution wherein there are a portion of higher temperature and a portion of lower temperature is formed in the complexly curved glass plate. Thus, in such case of turning of the complexly curved glass plate, there are disadvantages that the complexly curved glass plate can not uniformly be quenched and that the complexly curved glass plate may be broken due to a tensile stress or a compressive stress caused by a temperature distribution.
The present invention has been achieved in view of the problems in the conventional technique and to provide a method and an apparatus for bend-shaping a glass plate which avoids the turning of a complexly curved glass plate; equalizes substantially a temperature distribution in the complexly curved glass plate when it is cooled in a cooling device; and prevents a deformation of the complexly curved glass plate.